11.Lect 16-17control Statdfv

7/28/2019 11.Lect 16-17control Statdfv

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Control Statements

The C language programs until now followsa sequential form of execution ofstatements.

Many times it is required to alter the flow of

the sequence of instructions. C language provides statements that can

alter the flow of a sequence of instructions.These statements are called controlstatements.

These statements help to jump from onepart of the program to another. The controltransfer may be conditional orunconditional.


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C ProgrammingControl Statements

Lecture 16-17

Mohit Arora

Lecturer , LIECA

LPU


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If Statement

The if . then . else statement can beused with or without the else.

The two forms are:

if (expression)

statement1

if (expression)statement1

else

statement2

In both cases, when the expression is true, then statement1 isexecuted.

If the expression is false, then, in the first case, statement1 is skipped(not executed)

In the second case, statement2 after the else is executed.


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The simplest form of the control statement is the If statement.It is very frequently used in decision making and allowing theflow of program execution.

The If structure has the following syntax

if (condition)statement;

The statement is any valid C language statement and thecondition is any valid C language expression, frequentlylogical operators are used in the condition statement.

The condition part should not end with a semicolon, since the

condition and statement should be put together as a singlestatement.

If the condition is true then perform the following statement orIf the condition is fake the computer skips the statement andmoves on to the next instruction in the program.


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# include //Include the stdio.h file

void main () // start of the program

{

int numbers; // declare the variables

printf ("Type a number:"); // message to the userscanf ("%d", &number); // read the number from standard input

if (number < 0) // check whether the number is a negative number{

printf ("The value is %d \n", number); // print the value}getch();}


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If Statement

body of if

testexpression

exit

true


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IF-ELSE

The if else is actually just on extension of thegeneral format of if statement.

If the result of the condition is true, thenprogram statement 1 is executed, otherwise

program statement 2 will be executed. If any case either program statement 1 is

executed or program statement 2 is executedbut not both

When writing programs this else statement isso frequently required that almost allprogramming languages provide a specialconstruct to handle this situation.


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IfElse Statement

if (a>b)

{

}

else

{

}

the if part is executed if the test statement is

true, otherwise the else part is executed.


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If Else Statement

body of if

testexpression

exit

true

false

body of else


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IfElse Statement#include //include the stdio.h header file in your program

void main () // start of the main

{

int num; // declare variable num as integer

printf ("Enter the number"); // message to the user

scanf ("%d", &num); // read the input number from keyboard

if (num < 0) // check whether number is less than zero

{

printf ("The number is negative"); // if it is less than zero then it is negative

}

else // else statement

{

printf ("The number is positive"); // if it is more than zero then the given number ispositive

}

getch();

}


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Compound Relational test C language provides the mechanisms necessary to perform

compound relational tests A compound relational test is simple one or more simple

relational tests joined together by either the logical AND or thelogical OR operators. The compound operators can be used toform complex expressions in C.

Syntax

if (condition1 && condition2 && condition3)

The syntax in the statement a represents a complex ifstatement which combines different conditions using the andoperator in this case if all the conditions are true only then thewhole statement is considered to be true. Even if one condition

is false the whole if statement is considered to be false.


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b> if (condition1 || condition2 || condition3) The statement b uses the logical operator or (||) to

group different expression to be checked. In thiscase if any one of the expression if found to be truethe whole expression considered to be true, we

can also uses the mixed expressions using logicaloperators and and or together.


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Nested if Statement The if statement may itself contain another if statement is known as

nested if statement.

Syntax:

if (condition1)

if (condition2)statement-1;

else

statement-2;elsestatement-3;

The if statement may be nested as deeply as you need to nest it. Oneblock of code will only be executed if two conditions are true. Condition1 is tested first and then condition 2 is tested.

The second if condition is nested in the first. The second if condition is tested only when the first condition is true

else the program flow will skip to the corresponding else statement.


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Nested IfElse Statement#include

#include

void main(){

int a=12,b=13,c=15;

if (a>b)

{

if (b>c)

{

printf(sorted = %d %d %d\n,a,b,c);

}

else if (a>c)

{

printf(sorted = %d %d %d\n,a,c,b);

}

else

printf(sorted = %d %d %d\n,c,a,b);

}

else

{

if (a>c)

printf(sorted = %d %d %d\n,b,a,c);

else


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Switch Statement the switch statement is used if there are more than

two alternatives and the decision depends on the valueof the same variable

the switch statement can replace a ladder of multiplenested if..else statements

switch()

{

case :

break;

case :

break;

default :

}


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Switch Statement

variableequalsconst 1

exit

true

false

first case body

variableequalsconst 2

true

false

second case body

default body


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Switch Statement

char c;printf(Enter your choice (a/b/c) : );

Scanf(%c,&c);

switch (c)

{

case a:printf(You picked a!\n);

break;

case b:

printf(You picked b!\n);

break;case c:

printf(You picked c!\n);

break;

default:

printf(You picked neither a,b,c !\n);

}


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goto statementThe goto statement is a control flow statementthat causes the CPU to jump to another spot in the

code.

This spot is identified through use of a statementlabel.

The goto statement and its corresponding

statement label must appear in the same function.


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Jumps

Forward jump Backward jump

FORWARD JUMP

goto label:

----------------

----------------

label:

statement;

BACKWARD JUMP

label:

statement;

---------------------------------------

goto label;


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#include

#include

void main (){

int n=10;

loop:printf(value is :%d, n);n--;

if(n>0)goto loop;

printf("Done!);getch();

}


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The primary problem with goto is that it

allows a programmer to cause the point

of execution to jump around the codearbitrarily.

There are some restrictions on goto

use. For example, you cant jumpforward over a variable thats initialized

in the same block as the goto


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drawback of goto statement

#include#includevoid main()

{

int x ;

printf(Enter the value);scanf(%d,&x);

getch();}

11.Lect 16-17control Statdfv

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